1. Field of the Invention
The present invention relates to a ball slideway which is used as a guide for linear movement of a bed of a machine tool or the like, and more particularly to a ball slideway suitable for supporting large loads.
2. Description of the Prior Art
For enhancement of the working efficiency of a machine tool, it is necessary to increase the moving speed of a work table which is slidably mounted on the bed. Accordingly, it is important to reduce the sliding resistance between the bed and the work table.
As a solution to this problem, the prior art generally employs a straight antifriction bearing, an example of which is shown in FIGS. 1 to 3. FIG. 1 shows in perspective the external appearance of a ball slideway using the straight antifriction bearing and FIG. 2 is its side view. In FIGS. 1, 2 and 3, reference numeral 1 indicates a bed; 2 designates a work table; 3 identifies brackets; and 4 and 5 denote caterpillar type ball slides. In the bed 1 there are provided a pair of rectangular guide members 6 the surfaces of which have been hardened. The brackets 3 each have a cross section surrounding the guide member 6 and they are mounted on the work table 2 at four corners thereof. The caterpillar type ball slides 4 are disposed between each bracket 3 and the top and bottom surfaces of each guide member 6, and the caterpiller type ball slides 5 are disposed between the bracket 3 and both sides of the guide member 6. The caterpillar type ball slides 4 and 5 each have a cross section as depicted in FIG. 3 and they are installed in such a manner as to apply a preload to each ball 7. When the work table 2 is moved in the direction of the arrows A and A' in FIG. 1, the balls 7 of the caterpillar ball slides 4 and 5 circulate, while rolling, along a circulatory path formed by upper guide grooves 4a and 5a and lower guide grooves 4b and 5b. By such circulation of the balls 7 while rolling, the work table 2 is slidably supported without play on the guide members 6 of the bed 1 and the sliding resistance is small.
However, the conventional ball slideway having such a construction and an operation has a defect in that the load capacity is small because the ball guide surfaces of the guide grooves 4a and 5a and the guide members 6 are all flat.
This problem can be solved by employing rollers in place of the balls. However, although the load capacity increases, the adjustment of the preload is not as easy as with balls, in which case use is made of elastic deformation of the balls. Further, in either case, it is necessary to form ball or roller slides in four guide surfaces of the guide members so as to provide load capacity for loads acting on the guide members in all directions; this inevitably leads to complexity in structure. In addition, working of the ball slides 4 and 5 is troublesome.